1. Field of the Invention
The invention relates to an apparatus for medical diagnosis and/or therapy, including a detection device for detecting the presence of an object in the vicinity of a movable part of the apparatus, which detection device includes a number of proximity sensors which are mounted on the movable part and each of which is arranged to detect the presence of an object in the vicinity of the relevant sensor, means for forming a detection output signal of each of the proximity sensors, a drive unit for driving the movement of the movable part of the apparatus, and control means for controlling the drive unit in dependence on the detection output signals.
2. Description of the Related Art
An apparatus of this kind is known from United States Patent Specification U.S. Pat No. 4,987,583.
An apparatus for medical diagnosis and/or therapy may include a radiation transmitter and a radiation receiver. An example in this respect is a medical X-ray apparatus provided with an X-ray source and an X-ray receiver which is usually constructed as an X-ray image intensifier. These two elements are arranged at some distance from one another, the patient to be examined or treated being arranged between the X-ray source and the image intensifier. The X-ray source and the image intensifier are positioned relative to the body of the patient in such a manner that an image can be formed of the desired slice of the body (the "object"). The orientation and position of such apparatus can often be adjusted by means of a motor drive. Generally speaking, in the context of the present invention an object is to be understood to mean the body of a patient to be examined or another object to be examined, the body or a part of the body of a person operating the apparatus, parts of the apparatus itself (for example, the patient table) or of neighbouring apparatus, or other obstacles which could move into the path of movement of the parts of the apparatus.
Such apparatus often comprise a so-called C-arm, i.e. a circular support which is rotatable in its own plane via a guide or trackway (i.e. about an axis extending perpendicularly to the plane in which the C-arm is situated), which plane is rotatable about an axis situated in said plane. In many cases a number of other possibilities for displacement are also provided.
During use of the apparatus it is important that a movable part, for example the image intensifier, closely approaches the object to be examined in order to achieve the desired image sharpness. The image intensifier has a comparatively large front face for receiving the X-rays and each point on this front face or on its circumference can come into contact with the object to be examined. Such a collision can occur in any direction of movement of the image intensifier. This is undesirable and, therefore, such an apparatus comprises a detection device for detecting the presence of an object in the vicinity of the movable part of the apparatus.
It is important to provide such a detection device notably in the case of motor-driven apparatus. When the presence of an object is detected within a given small distance from the movable part of the apparatus, the movement of (that part of) the apparatus can be stopped so as to avoid a collision.
The cited U.S. Pat. No. 4,987,583 discloses a medical X-ray apparatus which includes a number of separate collision sensors which are mounted on parts of the apparatus which could come into contact with obstacles. These sensors enable detection of the collisions between an obstacle and movable parts of the apparatus. The apparatus includes means ensuring that, after detection of a collision with an obstacle, the drive operates in a direction opposing the direction of collision, so that the movable part immediately backs away from the obstacle after a collision. The back-out movement is stopped as soon as the sensor no longer detects contact between the sensor and the obstacle. In order to avoid recurrent collisions after that and to achieve normal operation of the apparatus again, it is necessary for the operating staff to switch off the control system and subsequently switch it on again. Using this device it can be detected merely that a collision has occurred, but the device does not know the direction of the collision so that it cannot control the movable part of the apparatus to perform a clearing motion other than that which opposes the collision direction.